Properties of shared and exclusive locks:
- Shared Lock or Read Lock
- It is requested by transaction that wants to just read the value of data items.
- A shared lock on a data item does not allow an exclusive lock to be placed but permits any number of shared locks to be placed on that item.
- Exclusive Lock
- It is requested by a transaction on a data item that it needs to update.
- No other transaction can place either a shared lock or an exclusive lock on a data item that has been locked in an exclusive mode.
Locking as above results in a serialisable schedule.